1. Field of the Invention
The present invention relates to a fuel cell system provided with a polymer electrolyte fuel cell.
2. Discussion of Background
As a proton conductive polymer contained in a catalyst layer of a membrane/electrode assembly for a polymer electrolyte fuel cell, the following polymer (1) is usually used (Patent Document 1).
A polymer (1) having sulfonic acid groups (—SO3H groups) converted from —SO2F groups in a polymer having repeating units based on a compound represented by the following formula (m14) and repeating units based on tetrafluoroethylene (hereinafter referred to as TFE):CF2═CF(OCF2CFZ)mOp(CF2)nSO2F   (m14)wherein Z is a fluorine atom or a trifluoromethyl group, m is an integer of from 0 to 3, p is 0 or 1, and n is from 1 to 12, provided that m+p>0.
A polymer electrolyte fuel cell is required to be operated under high temperature (at least 90° C.) and low humidity conditions where the relative humidity of the reaction gas (fuel gas and oxidant gas) is low, or under no humidity conditions, in order to simplify the fuel cell system or to reduce the cost. For example, by operating a polymer electrolyte fuel cell under low or no humidity conditions, a humidifier can be downsized or omitted. Further, in fuel cell systems for automobiles, by operating a polymer electrolyte fuel cell under high temperature conditions, a radiator for cooling the polymer electrolyte fuel cell can be downsized. Further, in fuel cell systems for stationary use, by operating a polymer electrolyte fuel cell under high temperature conditions, water used for cooling the polymer electrolyte fuel cell can be recovered as hot water, and the hot water can be thereby used in various applications.
However, the power generation characteristics (such as output voltage) of conventional polymer electrolyte fuel cells in which the polymer (1) is used as a proton conductive polymer in a catalyst layer are insufficient under high temperature and low or no humidity conditions. Therefore, the conventional polymer electrolyte fuel cells are required to be operated under low temperature (about 80° C.) and high humidity conditions. Therefore, a relatively large size humidifier is required for conventional fuel cell systems. Further, for fuel cell systems for automobiles, a large size radiator is required. Further, for fuel cell systems for stationary use, since the temperature of hot water to be recovered is low, the application of the hot water is restricted.
Patent Document 1: Japanese Patent No. 3675473